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From aaron morton <aa...@thelastpickle.com>
Subject Re: Retrieving a column from a fat row vs retrieving a single row
Date Fri, 10 Jun 2011 04:19:05 GMT
Don't forget that reading at ONE may not mean that only 1 replica is involved in the request.

Any get or multiget (not range scan) read that runs with ReadRepair enabled will be sent to
all UP replicas. If the RR is disabled it will only be sent to as many replicas as needed
for the CL. For CL ONE the RR happens async to the request, this normally means after the
initial request has returned. 

So running with CL One *may* make the request return a little faster, but if RR is enabled
you are still asking the cluster to do the same amount of work. And if the client(s) is running
in a tight loop reading at ONE makes is easier for the client to overload the server as it
can send more work before the server has really finished the previous request. 

You can adjust the probability the RR will run in the yaml config. 

Hope that helps.  
    
-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 10 Jun 2011, at 00:37, Richard Low wrote:

> 2011/6/9 H├ęctor Izquierdo Seliva <izquierdo@strands.com>:
> 
>> Yeah, but if I have RF=3 then there are three nodes that can answer the
>> request right?
> 
> Yes, if you're happy to read ConsistencyLevel.ONE.


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